In this part components installed into electrical switchboard will be presented. These components are:
The design of this is also described in semestral project (see [22]), which is written by author of this thesis. The assembling was realised during the semestral project and this diploma thesis, which is extension of the semestral project.
The scheme of the electric circuit is in the attachment. The PLC system TECOMAT FOXTROT CP-1018 will be described in the separate chapter.
4.1 Variable-frequency drive Mitsubishi D700
It is for controlling of rotation speed of the asynchronous electric motors. The control of the rotation speed optimizes the process (of the circulation in the case of this thesis). It decreases operating costs. The variable-frequency drive (VFD) is used for changing of the frequency of the electric current. Variable-frequency drives are also known as adjustable-frequency drives (AFD), variable-speed drives (VSD), AC drives, microdrives or inverter drives. The variable-frequency drive has 3 main parts: rectifier, DC link and inverter. The rectifier rectifies alternating voltage to pulsing direct voltage. This pulsing direct voltage is stabilized and smoothed by the DC link and after it is passed to the inverter. The inverter generates alternating voltage with frequency what is proportional to wanted rotation speed of the electric motor. The variable-frequency drive Mitsubishi D700 (see Attachment 2) is suitable for driving one phase asynchronous motor up to 2.2 kW, so there are two devices used for driving the ventilator of the circulation and the ventilator of the waste air (see reference [5]). Figure 16 represents the block scheme of the variable-frequency drive.
Figure 16: Block scheme of VFD
Table 5 shows basic specification of the variable-frequency drive Mitsubishi D700.
Table 5: VFD Mitsubishi D700 specification [5]
Power supply (50/60Hz) 200–240 V Output range 0.1 kW–2.2 kW Protective structure IP20
Output frequency 0.2–400 Hz
4.2 Power supply 24 V DC Mean Well MDR-60-24
Power supply 24 V DC Mean Well MDR-60-24 is used for power supplying (see Attachment 2) of the PLC, NDIR sensors and temperature sensors. These electric loads have not higher consumption than 60 W, so this power supply is suitable (see reference [4]). Table 6 gives basic properties of the power supply 24 V DC Mean Well MDR-60-24.
Table 6: Properties of power supply 24 V DC Mean Well MDR-60-24 [4]
Input VAC from 85 V to 264 V
4.3 Residual-current device OEZ OLFI C10
Residual-current device (RCD) disconnects the electrical circuit when part of incoming current is lost by the accident. This accident can be caused by broken isolation or touch of human. Basic component of this device is differential transformer. This transformer watches difference between input and output current of the electrical circuit, what should be equal 0 A.
When the difference is more than 30 mA (in our case) the electrical circuit is disconnected. So it means that residual-current device is safety element in the electrical circuit. The using of the safety elements in electrical circuits is regulated by standards. The residual-current device
OEZ OLFI C10 was used in this thesis (see Attachment 2). This type is produced by the Czech company OEZ s.r.o., which it is a member of Siemens group (see reference [6]).
4.4 Temperature sensor Ni1000
Temperature sensor Ni1000 is a resistance temperature sensor. It means that it uses temperature properties of metal. In this case the metal medium is a nickel. There is a relation between resistance of the sensor and temperature. The range of measurement is from – 70 °C to 200 °C. This type of sensors has good accuracy and reaction on the change of temperature.
Next advantage is small size (see reference [9] for more information).
4.5 Non-Dispersive Infrared Radiation sensor ASCO
2-GD
The principle of the Non-Dispersive Infrared Radiation (NDIR) sensor was explained before in section 3.1.1. The NDIR sensor of the CO2 concentration ASCO2-GD produced by the Czech company Protoronix s.r.o. is used in this thesis. Chosen sensor has good accuracy and it is designated for measuring in air-conditioning pipes. The specifications of this sensor are presented bellow (see reference [11] for more information). The picture of the NDIR sensor ASCO2-GD is in the attachment 1. Table 7 presents basic parameters of the NDIR sensor ASCO2-GD.
Table 7: Parameters of the NDIR sensor ASCO2-GD [11]
Parameter Value Unit
Table 8 shows values of the output voltage of the NDIR sensor ASCO2-GD. This output voltage depends on CO2 concentration.
Table 8: Output voltage and CO2 concentration of the sensor ASCO2-GD [11]
Concentration
Figure 17 presents the graph of the linear dependence of the output voltage of the NDIR sensor ASCO2-GD on the CO2 concentration.
Figure 17: Output voltage and CO2 concentration of the sensor ASCO2-GD [11]
In this realization it is necessary to modify the range of the output voltage of the sensor, because there is no input port into the used PLC TECOMAT FOXTROT CP-1018 with range 0–10 V, there are only input ports with range 0–1 V or 0–2 V. The modification is made by voltage divider. The equation (1) describes how to compute modified voltage (Um) of the voltage divider. The output voltage of the NDIR sensor (U) is modified. Resistor (R1) is divided as it is shown in the Figure 18. Rc represents all of resistors in the voltage divider.
Rc U R
Um 1
(1)
Figure 18 shows the realization with five 1 kΩ resistors. This realization is used in case of this thesis. It is possible to use other resistors, but the equation (1) must be valid.
Figure 18: The voltage divider scheme